diff --git a/Documentation/usb/functionfs-desc.rst b/Documentation/usb/functionfs-desc.rst
new file mode 100644
index 000000000000..39649774da54
--- /dev/null
+++ b/Documentation/usb/functionfs-desc.rst
@@ -0,0 +1,39 @@
+======================
+FunctionFS Descriptors
+======================
+
+Some of the descriptors that can be written to the FFS gadget are
+described below. Device and configuration descriptors are handled
+by the composite gadget and are not written by the user to the
+FFS gadget.
+
+Descriptors are written to the "ep0" file in the FFS gadget
+following the descriptor header.
+
+.. kernel-doc:: include/uapi/linux/usb/functionfs.h
+   :doc: descriptors
+
+Interface Descriptors
+---------------------
+
+Standard USB interface descriptors may be written. The class/subclass of the
+most recent interface descriptor determines what type of class-specific
+descriptors are accepted.
+
+Class-Specific Descriptors
+--------------------------
+
+Class-specific descriptors are accepted only for the class/subclass of the
+most recent interface descriptor. The following are some of the
+class-specific descriptors that are supported.
+
+DFU Functional Descriptor
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When the interface class is USB_CLASS_APP_SPEC and the interface subclass
+is USB_SUBCLASS_DFU, a DFU functional descriptor can be provided.
+The DFU functional descriptor is a described in the USB specification for
+Device Firmware Upgrade (DFU), version 1.1 as of this writing.
+
+.. kernel-doc:: include/uapi/linux/usb/functionfs.h
+   :doc: usb_dfu_functional_descriptor
diff --git a/Documentation/usb/functionfs.rst b/Documentation/usb/functionfs.rst
index d05a775bc45b..f7487b0d8057 100644
--- a/Documentation/usb/functionfs.rst
+++ b/Documentation/usb/functionfs.rst
@@ -25,6 +25,8 @@ interface numbers starting from zero).  The FunctionFS changes
 them as needed also handling situation when numbers differ in
 different configurations.
 
+For more information about FunctionFS descriptors see :doc:`functionfs-desc`
+
 When descriptors and strings are written "ep#" files appear
 (one for each declared endpoint) which handle communication on
 a single endpoint.  Again, FunctionFS takes care of the real
diff --git a/Documentation/usb/index.rst b/Documentation/usb/index.rst
index 27955dad95e1..826492c813ac 100644
--- a/Documentation/usb/index.rst
+++ b/Documentation/usb/index.rst
@@ -11,6 +11,7 @@ USB support
     dwc3
     ehci
     functionfs
+    functionfs-desc
     gadget_configfs
     gadget_hid
     gadget_multi
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index d8b096859337..ba5c6e4827ba 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -2478,7 +2478,7 @@ typedef int (*ffs_os_desc_callback)(enum ffs_os_desc_type entity,
 
 static int __must_check ffs_do_single_desc(char *data, unsigned len,
 					   ffs_entity_callback entity,
-					   void *priv, int *current_class)
+					   void *priv, int *current_class, int *current_subclass)
 {
 	struct usb_descriptor_header *_ds = (void *)data;
 	u8 length;
@@ -2535,6 +2535,7 @@ static int __must_check ffs_do_single_desc(char *data, unsigned len,
 		if (ds->iInterface)
 			__entity(STRING, ds->iInterface);
 		*current_class = ds->bInterfaceClass;
+		*current_subclass = ds->bInterfaceSubClass;
 	}
 		break;
 
@@ -2559,6 +2560,12 @@ static int __must_check ffs_do_single_desc(char *data, unsigned len,
 			if (length != sizeof(struct ccid_descriptor))
 				goto inv_length;
 			break;
+		} else if (*current_class == USB_CLASS_APP_SPEC &&
+			   *current_subclass == USB_SUBCLASS_DFU) {
+			pr_vdebug("dfu functional descriptor\n");
+			if (length != sizeof(struct usb_dfu_functional_descriptor))
+				goto inv_length;
+			break;
 		} else {
 			pr_vdebug("unknown descriptor: %d for class %d\n",
 			      _ds->bDescriptorType, *current_class);
@@ -2621,6 +2628,7 @@ static int __must_check ffs_do_descs(unsigned count, char *data, unsigned len,
 	const unsigned _len = len;
 	unsigned long num = 0;
 	int current_class = -1;
+	int current_subclass = -1;
 
 	for (;;) {
 		int ret;
@@ -2640,7 +2648,7 @@ static int __must_check ffs_do_descs(unsigned count, char *data, unsigned len,
 			return _len - len;
 
 		ret = ffs_do_single_desc(data, len, entity, priv,
-			&current_class);
+			&current_class, &current_subclass);
 		if (ret < 0) {
 			pr_debug("%s returns %d\n", __func__, ret);
 			return ret;
diff --git a/include/uapi/linux/usb/ch9.h b/include/uapi/linux/usb/ch9.h
index 44d73ba8788d..91f0f7e214a5 100644
--- a/include/uapi/linux/usb/ch9.h
+++ b/include/uapi/linux/usb/ch9.h
@@ -254,6 +254,9 @@ struct usb_ctrlrequest {
 #define USB_DT_DEVICE_CAPABILITY	0x10
 #define USB_DT_WIRELESS_ENDPOINT_COMP	0x11
 #define USB_DT_WIRE_ADAPTER		0x21
+/* From USB Device Firmware Upgrade Specification, Revision 1.1 */
+#define USB_DT_DFU_FUNCTIONAL		0x21
+/* these are from the Wireless USB spec */
 #define USB_DT_RPIPE			0x22
 #define USB_DT_CS_RADIO_CONTROL		0x23
 /* From the T10 UAS specification */
@@ -329,9 +332,10 @@ struct usb_device_descriptor {
 #define USB_CLASS_USB_TYPE_C_BRIDGE	0x12
 #define USB_CLASS_MISC			0xef
 #define USB_CLASS_APP_SPEC		0xfe
-#define USB_CLASS_VENDOR_SPEC		0xff
+#define USB_SUBCLASS_DFU			0x01
 
-#define USB_SUBCLASS_VENDOR_SPEC	0xff
+#define USB_CLASS_VENDOR_SPEC		0xff
+#define USB_SUBCLASS_VENDOR_SPEC		0xff
 
 /*-------------------------------------------------------------------------*/
 
diff --git a/include/uapi/linux/usb/functionfs.h b/include/uapi/linux/usb/functionfs.h
index 9f88de9c3d66..2ebdba111a8f 100644
--- a/include/uapi/linux/usb/functionfs.h
+++ b/include/uapi/linux/usb/functionfs.h
@@ -3,6 +3,7 @@
 #define _UAPI__LINUX_FUNCTIONFS_H__
 
 
+#include <linux/const.h>
 #include <linux/types.h>
 #include <linux/ioctl.h>
 
@@ -37,6 +38,31 @@ struct usb_endpoint_descriptor_no_audio {
 	__u8  bInterval;
 } __attribute__((packed));
 
+/**
+ * struct usb_dfu_functional_descriptor - DFU Functional descriptor
+ * @bLength:		Size of the descriptor (bytes)
+ * @bDescriptorType:	USB_DT_DFU_FUNCTIONAL
+ * @bmAttributes:	DFU attributes
+ * @wDetachTimeOut:	Maximum time to wait after DFU_DETACH (ms, le16)
+ * @wTransferSize:	Maximum number of bytes per control-write (le16)
+ * @bcdDFUVersion:	DFU Spec version (BCD, le16)
+ */
+struct usb_dfu_functional_descriptor {
+	__u8  bLength;
+	__u8  bDescriptorType;
+	__u8  bmAttributes;
+	__le16 wDetachTimeOut;
+	__le16 wTransferSize;
+	__le16 bcdDFUVersion;
+} __attribute__ ((packed));
+
+/* from DFU functional descriptor bmAttributes */
+#define DFU_FUNC_ATT_CAN_DOWNLOAD	_BITUL(0)
+#define DFU_FUNC_ATT_CAN_UPLOAD		_BITUL(1)
+#define DFU_FUNC_ATT_MANIFEST_TOLERANT	_BITUL(2)
+#define DFU_FUNC_ATT_WILL_DETACH	_BITUL(3)
+
+
 struct usb_functionfs_descs_head_v2 {
 	__le32 magic;
 	__le32 length;
@@ -104,23 +130,38 @@ struct usb_ffs_dmabuf_transfer_req {
 
 #ifndef __KERNEL__
 
-/*
+/**
+ * DOC: descriptors
+ *
  * Descriptors format:
  *
+ * +-----+-----------+--------------+--------------------------------------+
  * | off | name      | type         | description                          |
- * |-----+-----------+--------------+--------------------------------------|
+ * +-----+-----------+--------------+--------------------------------------+
  * |   0 | magic     | LE32         | FUNCTIONFS_DESCRIPTORS_MAGIC_V2      |
+ * +-----+-----------+--------------+--------------------------------------+
  * |   4 | length    | LE32         | length of the whole data chunk       |
+ * +-----+-----------+--------------+--------------------------------------+
  * |   8 | flags     | LE32         | combination of functionfs_flags      |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | eventfd   | LE32         | eventfd file descriptor              |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | fs_count  | LE32         | number of full-speed descriptors     |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | hs_count  | LE32         | number of high-speed descriptors     |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | ss_count  | LE32         | number of super-speed descriptors    |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | os_count  | LE32         | number of MS OS descriptors          |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | fs_descrs | Descriptor[] | list of full-speed descriptors       |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | hs_descrs | Descriptor[] | list of high-speed descriptors       |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | ss_descrs | Descriptor[] | list of super-speed descriptors      |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | os_descrs | OSDesc[]     | list of MS OS descriptors            |
+ * +-----+-----------+--------------+--------------------------------------+
  *
  * Depending on which flags are set, various fields may be missing in the
  * structure.  Any flags that are not recognised cause the whole block to be
@@ -128,71 +169,111 @@ struct usb_ffs_dmabuf_transfer_req {
  *
  * Legacy descriptors format (deprecated as of 3.14):
  *
+ * +-----+-----------+--------------+--------------------------------------+
  * | off | name      | type         | description                          |
- * |-----+-----------+--------------+--------------------------------------|
+ * +-----+-----------+--------------+--------------------------------------+
  * |   0 | magic     | LE32         | FUNCTIONFS_DESCRIPTORS_MAGIC         |
+ * +-----+-----------+--------------+--------------------------------------+
  * |   4 | length    | LE32         | length of the whole data chunk       |
+ * +-----+-----------+--------------+--------------------------------------+
  * |   8 | fs_count  | LE32         | number of full-speed descriptors     |
+ * +-----+-----------+--------------+--------------------------------------+
  * |  12 | hs_count  | LE32         | number of high-speed descriptors     |
+ * +-----+-----------+--------------+--------------------------------------+
  * |  16 | fs_descrs | Descriptor[] | list of full-speed descriptors       |
+ * +-----+-----------+--------------+--------------------------------------+
  * |     | hs_descrs | Descriptor[] | list of high-speed descriptors       |
+ * +-----+-----------+--------------+--------------------------------------+
  *
  * All numbers must be in little endian order.
  *
  * Descriptor[] is an array of valid USB descriptors which have the following
  * format:
  *
+ * +-----+-----------------+------+--------------------------+
  * | off | name            | type | description              |
- * |-----+-----------------+------+--------------------------|
+ * +-----+-----------------+------+--------------------------+
  * |   0 | bLength         | U8   | length of the descriptor |
+ * +-----+-----------------+------+--------------------------+
  * |   1 | bDescriptorType | U8   | descriptor type          |
+ * +-----+-----------------+------+--------------------------+
  * |   2 | payload         |      | descriptor's payload     |
+ * +-----+-----------------+------+--------------------------+
  *
  * OSDesc[] is an array of valid MS OS Feature Descriptors which have one of
  * the following formats:
  *
+ * +-----+-----------------+------+--------------------------+
  * | off | name            | type | description              |
- * |-----+-----------------+------+--------------------------|
+ * +-----+-----------------+------+--------------------------+
  * |   0 | inteface        | U8   | related interface number |
+ * +-----+-----------------+------+--------------------------+
  * |   1 | dwLength        | U32  | length of the descriptor |
+ * +-----+-----------------+------+--------------------------+
  * |   5 | bcdVersion      | U16  | currently supported: 1   |
+ * +-----+-----------------+------+--------------------------+
  * |   7 | wIndex          | U16  | currently supported: 4   |
+ * +-----+-----------------+------+--------------------------+
  * |   9 | bCount          | U8   | number of ext. compat.   |
+ * +-----+-----------------+------+--------------------------+
  * |  10 | Reserved        | U8   | 0                        |
+ * +-----+-----------------+------+--------------------------+
  * |  11 | ExtCompat[]     |      | list of ext. compat. d.  |
+ * +-----+-----------------+------+--------------------------+
  *
+ * +-----+-----------------+------+--------------------------+
  * | off | name            | type | description              |
- * |-----+-----------------+------+--------------------------|
+ * +-----+-----------------+------+--------------------------+
  * |   0 | inteface        | U8   | related interface number |
+ * +-----+-----------------+------+--------------------------+
  * |   1 | dwLength        | U32  | length of the descriptor |
+ * +-----+-----------------+------+--------------------------+
  * |   5 | bcdVersion      | U16  | currently supported: 1   |
+ * +-----+-----------------+------+--------------------------+
  * |   7 | wIndex          | U16  | currently supported: 5   |
+ * +-----+-----------------+------+--------------------------+
  * |   9 | wCount          | U16  | number of ext. compat.   |
+ * +-----+-----------------+------+--------------------------+
  * |  11 | ExtProp[]       |      | list of ext. prop. d.    |
+ * +-----+-----------------+------+--------------------------+
  *
  * ExtCompat[] is an array of valid Extended Compatiblity descriptors
  * which have the following format:
  *
+ * +-----+-----------------------+------+-------------------------------------+
  * | off | name                  | type | description                         |
- * |-----+-----------------------+------+-------------------------------------|
+ * +-----+-----------------------+------+-------------------------------------+
  * |   0 | bFirstInterfaceNumber | U8   | index of the interface or of the 1st|
+ * +-----+-----------------------+------+-------------------------------------+
  * |     |                       |      | interface in an IAD group           |
+ * +-----+-----------------------+------+-------------------------------------+
  * |   1 | Reserved              | U8   | 1                                   |
+ * +-----+-----------------------+------+-------------------------------------+
  * |   2 | CompatibleID          | U8[8]| compatible ID string                |
+ * +-----+-----------------------+------+-------------------------------------+
  * |  10 | SubCompatibleID       | U8[8]| subcompatible ID string             |
+ * +-----+-----------------------+------+-------------------------------------+
  * |  18 | Reserved              | U8[6]| 0                                   |
+ * +-----+-----------------------+------+-------------------------------------+
  *
  * ExtProp[] is an array of valid Extended Properties descriptors
  * which have the following format:
  *
+ * +-----+-----------------------+------+-------------------------------------+
  * | off | name                  | type | description                         |
- * |-----+-----------------------+------+-------------------------------------|
+ * +-----+-----------------------+------+-------------------------------------+
  * |   0 | dwSize                | U32  | length of the descriptor            |
+ * +-----+-----------------------+------+-------------------------------------+
  * |   4 | dwPropertyDataType    | U32  | 1..7                                |
+ * +-----+-----------------------+------+-------------------------------------+
  * |   8 | wPropertyNameLength   | U16  | bPropertyName length (NL)           |
+ * +-----+-----------------------+------+-------------------------------------+
  * |  10 | bPropertyName         |U8[NL]| name of this property               |
+ * +-----+-----------------------+------+-------------------------------------+
  * |10+NL| dwPropertyDataLength  | U32  | bPropertyData length (DL)           |
+ * +-----+-----------------------+------+-------------------------------------+
  * |14+NL| bProperty             |U8[DL]| payload of this property            |
+ * +-----+-----------------------+------+-------------------------------------+
  */
 
 struct usb_functionfs_strings_head {
